1. Field of the Invention
The present invention relates to an image processing apparatus that applies film grain-like effects in silver-salt photography to digital image data and to a method for controlling the image processing apparatus.
2. Description of the Related Art
In recent years, in order to achieve film grain effects as a way to express photographs taken using digital cameras, a method for combining noise as film grain has been suggested. In the technique described in Japanese Patent Laid-Open No. 11-085955, grain patterns are scanned and acquired from color films or false color cloud density patterns are acquired by simulation. The acquired patterns are arranged at random positions or arranged with certain distances therebetween in accordance with a desired image size. In the technique described in U.S. patent application Ser. No. 07/922,701, grain patterns having different densities and sizes are prepared in advance, and grain patterns selected in accordance with received signals are combined together and are projected to a monitor.
However, in a method like Japanese Patent Laid-Open No. 11-085955 in which grain patterns prepared in advance are arranged in accordance with an image size, it is visible that a noise pattern is attached in the size of a grain pattern prepared in advance, thus generating an unnatural image causing a viewer to feel strange. In terms of an output size of a digital camera, if grains of images in output sizes having different numbers of pixels are not set to have optimal sizes, the granularity of an image differs depending on the size of the image when being viewed. In addition, in a method like U.S. patent application Ser. No. 07/922,701 in which grain patterns having different densities and sizes are prepared in advance and grain patterns selected in accordance with received signals are combined together, it is necessary to prepare a great number of different types of grain patterns. If a great number of different types of grain patterns are not prepared in advance, a situation in which the same grain pattern frequently used in a plurality of photographing operations becomes like fixed pattern noise occurs, thus generating an unnatural image causing a viewer to feel strange, in particular, for a case of movies captured. In addition, since the memory capacity of a digital camera is limited, it is difficult to store film grain data corresponding to the entire image having a desired size.